With help from human genes, cows can now make enhanced milk with health-promoting properties that resemble those of human breast milk.
The development is an incremental advance in a long-standing goal to produce transgenic milk with nutraceutical powers, said an expert in the field. Still, the new study brings scientists another step closer to finding a safe and easy way of making milk that could battle debilitating diarrhea in millions of children in the developing world.
Eventually, the research might also help people with Crohn's Disease, Irritable Bowel Syndrome and other gastrointestinal problems.
And while some headlines have touted the discovery as a way to get human breast milk out of the udders of dairy cows, this kind of transgenic milk is still far more cow-like than human-like. It simply contains a boosted level of beneficial enzymes, much like the milk that human mothers produce.
"The cows are making cow's milk that has a human protein in it," said James Murray, a geneticist in the animal science department at the University of California, Davis, who has done similar work with goats but was not affiliated with the new study. "To say it is more like human milk is stretching it a little bit. I think that's misleading. It also just plays into the fears of people who are opposed to it."
Human breast milk is known to have a number of beneficial qualities for babies. It helps their gastrointestinal tracts develop and mature. It aids in the development of a beneficial population of bacteria in their guts. And it raises the levels of anti-inflammatory molecules in their bodies, making them better able to resist infections.
A countless number of nutrients and other components combine to make breast milk so healthful for babies. But scientists working decades ago zeroed in on two enzymes. Called lysozyme and lactoferrin, both contribute to the antimicrobial and anti-inflammatory powers of human milk. And both are far more abundant in human milk than in the milk of other animals.
There is, for example, 3,000 times more lysozyme in human milk than in cow's milk. Levels are 1,600 times higher in human milk than in goat's milk.
Some 20 years ago, researchers managed to isolate the genes that make these enzymes. Then, they began putting the genes into ruminants, with the goal of getting the animals to produce enzyme-enhanced milk.
Among other advances, scientists have already engineered cows that secrete extra lactoferrin into their milk. And Davis' group has developed transgenic goats that have 270 times more lysozyme in their milk than normal. His team has also fed their transgenic goat milk to young pigs -- equivalent in age to human preschoolers -- and documented improved gastrointestinal health as a result.
For the new study, Ning Li, of China Agricultural University in Beijing, and colleagues used standard genetic cloning techniques. They began with easy-to-acquire human genes that both make lysozyme and regulate its expression. They put those genes into cow cells, and they created embryos that contained those genes in their mammary glands.
The study yielded 17 healthy adult cattle that secreted 25 times more lysozyme into their milk than normal cows do, the researchers reported in the journal PLoS One.
"To our knowledge, this is the first study that resulted in the production of a herd of cloned transgenic cattle that expressed" the lysozyme gene in their milk, the researchers wrote. "It is fulfilled the conception of humanizing the bovine milk."
Five million children contract debilitating diarrhea around the world each year, Murray said, and half of those die from dehydration and related problems. With its gut-focused benefits, transgenic milk might eventually be able to save many of those children. And cows offer a promising factory because they produce such large quantities of milk.
The milk would likely be safe, Murray added. Even with its elevated enzyme levels, two glasses of even the most enhanced transgenic milk still contains far less lysozyme than we swallow in our saliva every day.
Before the milk will ever make it to market, though, researchers will need to conduct clinical studies in animals and people to prove its safety and its ability to heal the gut. For now, the research still has a long way to go, said Steven Miles, professor of medicine and bioethicist at the University of Minnesota, Twin Cities.
"This is very much a halfway technology," Miles said. "Human milk contains an enormous number of proteins that are beneficial. To highlight one particular protein -- in this case the lysozyme as justifying any kind of substitution of cow's milk for human milk would be a pretty reckless thing to do."
While transgenic technologies hold plenty of promise, he added, there are also risks that need to be considered. And in this case of milk, he thinks nature still has a leg up on genetic engineering.
"They're not producing human milk, they're producing a product that is inferior to human milk," Miles said.
© 2012 Discovery Channel